The elucidation of the cellular progenitors of neoplasia is an essential step in deciphering the mechanisms involved in chemical induced hepatocarcinogenesis. To this aim we will use immunochemical and immunocytothemical techniques in the proposed studies to characterize patterns of surface antigen expression on subpopulation of carcinogen altered cells. Monoclonal antibodies recognizing subpopulations of carcinogen altered liver cells induced in ACI rats by 2-acetylaminofluorene, diethylnitrosamine, 3-methyl-4-dimethylaminoazobenzene and ethionine will be produced. Reactive antigens isolated from detergent extracts of radiolabeled cells by immunoprecipitation will be characterized by a variety of methods including one and 2-dimensional polyacrylamide gel electrophoresis, one and 2-dimensional peptide mapping techniques, endoglycosidase digestion and lectin affinity chromatography. Immunofluorescent and immunoprecipitation assays will be used to determine patterns of surface antigen expression on carcinogen altered cells, fetal, newborn, and regenerating hepatocytes and primary and trasplantable hepatocellular carcinomas. Genotypic mosaic livers constructed by transplantation of carcinogen altered ACI rat liver cells in livers of (ACI x Le) F1 rats will be used to examine the biological potential of carcinogen altered cells with defined surface antigenic phenotypes. Genotypic mosaic livers will also be used as a model for immunotherapy to test the therapeutic potential of immunotoxins prepared by coupling pokeweed antiviral protein to monoclonal antibodies. These studies will contribute to our knowledge of the cellular lineages leading to hepatocellular carcinoma and will provide immunological probes which can be used for the histopathological assessment of carcinogen-induced hepatic lesions.